1. Field of the Invention
The present invention relates to a safety binding for interfacing a ski boot to a ski or skiboard. A skiboard is defined as a ski with an overall length of 100 cm or less.
2. Discussion of the Related Art
Skiboards have been offered for sale with non-releasable bindings for several years. Non-releasable bindings were justified for use on skis under 100 cm due to the reasonable belief that the limited length of the ski would limit loads on the skier's leg to safe levels. Recently available statistics now show that injuries to skiboarders, although not largely disproportionate to the overall injury rate among skiers, show a disproportionate number of the injuries to the lower leg. These injuries include spiral fractures of the tibia, a very common injury to skiers before the availability of well engineered releasable safety bindings for skis in the 1970's and 1980's. The development of releasable safety bindings for skis has practically eliminated lower leg fractures and therefore appropriately designed releasable safety bindings can reasonably be expected to practically eliminate the lower leg fractures seen among skiboarders.
Conventional safety bindings for skis are not suitable for use on ski boards or other short skis for a variety of reasons:
a. They are generally too long. The release mechanism is generally located in front of the toe and behind the heel of the boot. The running length of a skiboard is typically 65 cm. A boot/binding system is typically 60 cm.
b. The thickness required by the skiboard design will not allow enough thickness for the typical attachment screws that hold the toe piece and heel pieces to the ski.
c. The desirable flexibility of the extremities of the skiboard would compromise the function of conventional bindings that depend on the very stiff and stable platform typical of conventional skis and described by ASTM and ISO standards for compatibility.
d. Skiboards do not and probably cannot be reasonably designed to conform to the ASTM and ISO standards for binding mounting areas on skis. These standards were developed to make ski designs compatible with conventional binding designs.
Furthermore, since the basic configuration of safety bindings was developed in the 70's and 80's, when skiboards and very short adult skis did not exist, there is an opportunity to eliminate some of the design limitations and flaws that have been perpetuated by the various binding manufacturer.
Current trends in ski design are towards much shorter ski lengths. Even skis used by elite world-class racers are often less than 160 cm in length, with running lengths less than 135 cm. The binding mounting area controlled by ASTM and ISO compatibility standards is 60 cm long. That is approximately 45% of the running length of a 160 cm ski. Compromises must be made in order to design these short skis to conform to ASTM and ISO standards intended to assure compatibility with the various bindings on the market. If a binding could be designed to eliminate or reduce the constraints imposed by conventional binding designs then ski design could be advanced to a new performance level. There have in the past been some efforts to create bindings which would not impair the ability of a ski to flex, such as U.S. Pat. No. 5,129,668 (Hecht) and U.S. Pat. No. 5,671,939 (Pineau) both of which describe a system in which a mounting is provided for the ski binding, said mounting creating a raised surface for the binding while allowing the ski to flex to a full arc. These mounting however add to both the cost and the complexity of a binding since an entirely new part is added.
Mounting conventional bindings is a complex procedure that is normally done by certified professionals employed by ski shops and trained by specialists. If a binding could be designed to mount to metal inserts built into a ski in a standard insert pattern with machine screws then this complexity can be eliminated. This is the norm in the snowboard industry where bindings can be simply mounted by the consumer with nothing more than a Phillips screwdriver.
Controlling the effects of boot/binding friction on binding performance is one of the most, difficult factors of binding design. Shortcomings in how friction has been dealt with by designers of conventional bindings makes the adjustment of the binding to the boot, and confirmation that such adjustments will produce the desired release characteristics, a very complex task that is normally performed by certified professionals. This is due to the fact that most of the friction between the boot and the binding is not “sensed” by the release mechanism of the binding. Therefore, any variation in frictional forces produces a variation in release torque. The person adjusting the binding must understand this relationship to properly adjust the binding.
If a binding could be designed with a sensing mechanism that senses all the forces between the boot and the binding that result in a torque on the tibia then friction would not have to be controlled within very strict limits. Frictional loads would only have to be held below a value that is in the range of normal friction between a typical shoe sole and the ground since humans have evolved the strength to withstand such forces. All fictional forces not seen by the release mechanism would be contained within the binding mechanism and therefore would be subject to the control of the design engineers and of no concern to the person mounting and adjusting the binding. Boot binding adjustment would not be critical to binding performance and could potentially be undertaken by the consumer.
One solution which has been used in trying to solve this problem in the past are plate bindings. Plate bindings of various types have a plate which is either formed integral with the binding, U.S. Pat. No. 4,052,086 (Eckhart), U.S. Pat. No. 5,240,275 (Jungkind), U.S. Pat. No. 5,044,657 (Freisinger et al.), U.S. Pat. No. 4,893,831 (Pascal et al.), U.S. Pat. No. 4,892,326 (Svoboda et al.), U.S. Pat. No. 4,314,714 (Gertsch), and U.S. Pat. No. 4,073,509 (Gertsch) being examples of this type; or having a detachable plate which is fastened to the ski boot, as in U.S. Pat. No. 5,145,202 (Miller), U.S. Pat. No. 5,044,654 (Meyer), U.S. Pat. No. 4,395,055 (Teague, Jr.), U.S. Pat. No. 4,185,851 and U.S. Pat. No. 3,944,237. In both of these types of binding the designer attempts to take the unknown friction between the boot and the binding out of the picture by having the boot be fixed to a plate and leaving only a known friction between the plate and the binding.
Conventional bindings release by sensing a lateral force at the toe of the boot and cannot differentiate between loads at the tip of the ski and loads at the tail of the ski that produce the same torque about the tibial axis. For example, a release caused by a force on the lateral (outside) edge of the ski 70 cm in front of the tibial axis will subject the tibia and connective tissues to same torque but opposite shear load than if the same load where applied to the medial (inside) edge 70 cm behind the tibial axis. It is believed by many knowledgeable in the art of ski binding design and ski injury analysis that Anterior Cruciate Ligament (ACL) injuries to the knee are often caused by a load to the medial (inside) edge of the tail of the ski. This kind of load causes an abduction and inward twisting of the lower leg. If a binding could be designed that could differentiate between loads applied at the tip of the ski, outward twisting loads applied at the lateral side of the ski tail and inward twisting loads applied at the medial side the ski tail it may have the potential to afford skiers significant additional protection against ACL injuries that conventional bindings cannot provide.